Cationic and neutral heterometallic Ir-group 12 element polyhydride compounds: synthesis, structure and reactivity

The preparation and reactivity of some Ir–Zn and Ir–Cd heterometallic hydride complexes are described. Treatment of [Ir(IPr)₂H₂][BAr^F₄] (1; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene; Ar^F = 3,5-C₆H₃(CF₃)₂) with M′R₂ (M′ = Zn; R = Ph, Me, Et; M′ = Cd, R = Me) and Me₃SiCH=CH₂ results in dehydrogenation of an IPr isopropyl substituent, along with R–H elimination, to form square-pyramidal [Ir(IPr)(IPr″)(M′R)H][BAr^F₄] (M′R = ZnPh (4a); ZnMe (4b); ZnEt (4c); CdMe (8); IPr″ = dehydrogenated IPr) featuring apical M′R ligands. Heating 1 with 2 equiv ZnPh₂ under H₂ forms [Ir(IPr)₂(ZnPh)₂H₄][BAr^F₄] (5) featuring trans ZnPh ligands. Exposure of 4b-c and 8 to H₂ yields [Ir(IPr)(IPr″)(M′R)H₃][BAr^F₄] (9b-c, 10) as intermediates to highly fluxional [Ir(IPr)₂(M′R)(η²-H₂)H₃][BAr^F₄] (11b-c, 12). Reacting 11b–c with Lewis bases (L) effects [ZnR]⁺ abstraction to give pentahydride Ir(IPr)₂H₅ (13); with 11c and L = IMes (1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), [L₂ZnEt][BAr^F₄] was characterized, whereas with L = PMe₃, both 13 and [Ir(IPr)₂(ZnEt)(PMe₃)H₃][BAr^F₄] (14c) were formed. Reactions of 13 with M′R₂ similarly proceed with R–H elimination to form Ir(IPr)₂(M′R)H4 (15a-c, 16). Crystallographic and computational analyses characterize a range of hydride ligands, the nature of which depends subtly on the surrounding coordination environment. The new polyhydride complexes reported here add to the small number of such species featuring N-heterocyclic carbene ligands.